1. Field of the Invention
The invention relates generally to systems and methods for aligning or realigning a block specimen in a microtome.
2. Background
Scientists and medical professionals often analyze tissue from humans, animals, or other biological specimens in a microscopic examination to diagnose various diseases and conditions. One method of preparing these specimens for histological examination is through the use of a rotary (also known as a table microtome) or cryostat microtome. Microtomes are mechanical devices used to consistently create thin sections, typically between 5 and 10 μm, of biological specimens. When cutting on a rotary microtome, harvested specimens reside in blocks of paraffin, whereas in cryostat microtomes, specimens are embedded in optimal cutting temperature (OCT) frozen media. In contrast to the rotary microtome, the cryostat microtome has a microtome unit mounted in a cooling enclosure with externally mounted controls. After the specimens are sliced in either type of microtome, the sliced sections can be stained and examined.
Generally, in operation of a rotary or cryostat microtome, the block having the specimen (referred to herein as a “block specimen”) is secured to a chuck and clamped into the microtome. By fixing the chuck to the microtome, a user can align the block specimen along any of three planes (i.e., in X-, Y-, and Z-planes) in juxtaposition to a stationary thin knife (or blade). Once the block specimen is aligned with the knife, the user conducts a process known as “facing” or “truing” the block specimen.
During the truing process, the user operates a handwheel on the microtome to advance the block forward and vertically across the surface of the knife until complete sections of the block specimen are consistently sliced and the specimen itself is substantially exposed. Each rotation of the handwheel actuates mechanical gearing within the microtome to incrementally advance the block specimen forward for cutting the next (serial) section. Once the user obtains a desired sectioning surface and depth, the user can begin to slice sections for analysis. However, the conventional truing process has its limitations.
Slight misalignments of the block specimen to the knife or imperfections in the flatness of the block specimen's surface in juxtaposition to the knife can result in an incomplete section unsuitable for subsequent analysis. As slicing continues during the truing, incomplete sections or slices may contain specimen, as opposed to being entirely paraffin, and may be discarded. Furthermore, because many conventional microtomes allow the chuck to be adjusted in all three planes, it can be very challenging for sets of block specimens cut on a single microtome or for block specimens cut on different microtomes to have cutting planes that match in all three planes. For example, using a manual, time-consuming process, a user can attempt to align a block specimen by adjusting various angles of the chuck and then slicing a section with the knife to ascertain whether the block specimen's surface is substantially aligned with the cutting plane of the knife. This trial-and-error process is repeated until the user can slice a full section of the block. Moreover, microtomes are not designed to record the alignment angles by which a given block specimen resides within a chuck, so block specimens returning to a microtome for further slicing may require the user to conduct the time-consuming alignment process. Microtomes are also not engineered to automatically re-align the chuck to match the cutting planes of previously sectioned blocks, thereby requiring manual realignment by a user. As a result, the user may need to re-true the block each time it is positioned for slicing in a microtome. Manual realignment of the block can be very tedious and difficult. And sequential re-truing of blocks typically results in a substantial loss of sample before a complete section is properly sliced. Even those users who re-embed the entire block specimen or the specimen itself in a new block and then attempt to align the newly formed block specimen would similarly encounter these challenges.
Conventional attempts to align a block within a microtome are insufficient. For example, Microm's histo collimator attempts to align a block using a laser. In its general operation, the histo collimator uses a sight, a light source, and a mirror. The mirror is mounted on the surface of the block and reflects the light back to a crosshair in the sight. When a light beam from the light source is centered on the crosshair, the block is aligned in the horizontal and perpendicular planes. However, this equipment is very expensive and is operable on only Microm's microtomes. In another example of conventional equipment, such as those made by Newcomer Supply, Advanced Innovations, and Market Lab, a microtome aligner can set the microtome to zero in the X-, Y-, and Z-planes. If a plane is not set to zero, the block will not be properly aligned. For example, when using a block that was previously cut on a different microtome, the block aligned along a zero X-, Y-, and Z-plane of one microtome may not correlate to a zero X-, Y-, and Z-plane of another microtome. Additionally, a zero plane for a chuck holding a block does not necessarily correlate to a block surface perpendicular to the knife, so the block may require further alignment. This equipment is also expensive and is operable on only certain microtomes.
In addition to the disadvantages of the conventional equipment for aligning blocks in rotary microtomes, none of this conventional equipment is applicable to cryostat microtomes. Indeed, after over 100 years of advances in microtome technology, there still exists a need for accurately and consistently aligning and realigning block specimens in microtomes, as well as an alignment system or method that can be used on different types of microtomes.